Monday, February 17, 2014

Pond Herons

The current discussion on Pond Heron identification in the UK, triggered by the discovery of this bird, and this post on Birding Frontiers suggesting that Indian and Chinese Pond Herons may be separable in non-breeding plumage caught my attention.

Chinese PH is an abundant winter visitor to Thailand, whilst Javan PH is resident in some parts of the country, including Bangkok. When I first moved to Thailand I momentarily took an interest in the Pond Herons (because I wanted to tick both species!) but I had to wait until I saw birds coming into breeding plumage before I could convince myself; the received wisdom is that Javan and Chinese PH cannot be separated in non-breeding plumage, and the same message seems to go for Indian Pond Heron too. Indian PH is rare or very scarce in Thailand, but is reported more often these days (there is even a claim of breeding) perhaps due to greater awareness, but Javan also seems to be expanding its range, possibly as a result of larger areas of land under irrigation (Phil Round pers comm.).

This means that I've kept an interest in looking at Pond Herons in late winter/spring in the hope of finding an Indian PH on my patch, and indeed I found a crispy adult in April 2011. Then last July I found an "odd" Pond Heron which was suggested to me might be a hybrid Javan x Indian!

The whole issue about the the Pond Herons being unidentifiable to species in non-br plumage has always left me thinking "somebody is eventually going to figure these things out, it just needs some (perhaps a lot!) of effort" - the Birding Frontiers blog post made me think that Martin Garner and Ian Lewington might be on to something. Clearly Pond Herons present some interesting questions in terms of ID and range expansion.

Here are the main protagonists in breeding plumage, which is acquired by the pre-breeding moult of the body feathers and inner secondaries (del Hoyo et. al, 1992):

Chinese PH, 7th March 2009, Bangkok

Javan PH of the subspecies continentalis, 13th April 2011, Bangkok

Indian PH, 22nd April 2012, Bangkok (attaining maroon mantle)

putative hybrid (Javan x Indian?) Pond Heron, Bangkok, 2nd July 2013

The possibility of the bird above being a hybrid was based upon it appearing to have a head and neck colour closer to Indian PH, but the mantle and back being entirely dark grey (closer to Javan PH).

With regard to birds in transition from non-breeding to breeding plumage, Martin Garner in one of his BirdingFrontiers posts put out a request for photos of Pond Herons in February, so I was only too happy to contribute some images taken last week, and some text on my interpretation of each bird. The post can be seen here, and I have adpated the text below.

Bird 1: a fairly classic non-breeding PondHeron
spp, for which conventional thinking is that it cannot be done to
species. This bird appears to have clean wing coverts, so I'm guessing
it is an adult.

Bird 1

Bird 2: A few small patches of maroon appearing on the neck indicate that this is a Chinese PondHeron

Bird 2

Bird 3: A few small patches of maroon (note the one behind/below the eye) indicates that this is a Chinese PondHeron

Bird 3

Bird 3

Bird 4: This bird shows no indication of breeding
plumage (well, perhaps the whitish feather shafts on the bird's back?).
It was feeding in the same area as Bird 3, at the same time, and the
photos were taken from the same place, just a few seconds apart. When
comparing this image with Bird 3 (shot 2) I am particularly struck by
the difference in ground colour (bird 4 being much paler). Is this
within the range of variation of a single species? It looks like an
adult from the clean white wing coverts.

Bird 6: a Chinese PondHeron, the most advanced I saw yesterday in terms of its transition to breeding plumage

Bird 6

Bird 6

Bird 6

Bird 7: an adult bird based on the clear white wing
coverts, and definitely not Chinese, given the pale yellowish-buff
colours that are appearing on the neck. It could be Indian PH (a
rarity in Thailand), but the default species would be Javan PH. At
this stage I think it is too early to be certain. Javan seems to be
quite variable in the intensity of the neck colour, or perhaps it gets
darker as the breeding season progresses? I note that the ground colour
of this bird is very similar to Bird 4, which makes me think that bird 4
is the same species (ie probably Javan).

Bird 7

Bird 7

Bird 8: an apparent 2nd CY bird (dirty coverts). No indication of breeding plumage that I can see.

Bird 8

Bird 8

There are still several unknowns that I'm trying to figure out. These include:

What is the significance of "dirty" lesser coverts? Wells (1999) suggests that these are an indicator of 1CY/2CY birds.

There is significant variation in leg colour in the images that I have included above - most peculiar is the colour of the legs (which are pink) on the putative hybrid, whereas nearly all the other Pond Herons (Indian/Chinese/Javan) in images on Oriential Bird Images, and in my pictures have yellow legs, though interestingly a couple of photos on OBI from Thailand show breeding plumaged Javan Pond Herons with pink legs (see here and here). Leg colour seems to change in both Chinese PH and Javan PH during courtship (del Hoyo et. al, 1992; Round, 2008). What might the significance of this be?

Are there any differences in Pond Heron non-breeding plumages in autumn/early winter that will allow specific identification? This is the million dollar question! I'll be honest and say that in autumn I have always ignored Pond Herons in favour of hunting down interesting warblers and flycatchers on my patch, though counts of 50-100 Pond Herons on days in October have indicated to me that there is a significant passage (presumably of migrating Chinese PHs, rather than "sedentary" Javans, but perhaps there are some Indian PHs in there too?).

About Me

Bangkok-based patch-worker in Suan Rot Fai, a large park close to the city's famous weekend market. I have recorded 150 species on my patch since 2008. As one of the only big green spaces in the city, "SRF" acts as a real magnet for migrants during spring and autumn, and holds a healthy selection of "sibes" during the winter months.